Ultraviolet lamp systems, such as those used in the heating or curing of adhesives, sealants, inks or other coatings for example, are designed to couple microwave energy to an electrodeless lamp, such as an ultraviolet (UV) plasma lamp bulb mounted within a microwave chamber of the lamp system. In ultraviolet lamp heating and curing applications, one or more magnetrons are typically provided in the lamp system to couple microwave radiation to the plasma lamp bulb within the microwave chamber. The magnetrons are coupled to the microwave chamber through waveguides that include output ports connected to an upper end of the chamber. When the plasma lamp bulb is sufficiently excited by the microwave energy, it emits ultraviolet radiation through an open lamp face of the lamp system to irradiate a substrate which is located generally near the open lamp face.
A source of forced air is fluidly connected to a housing of the lamp system which contains the magnetrons, the microwave chamber and the plasma lamp bulb. The source of forced air is operable to direct cooling air, such as 350 CFM of cooling air for example, through the housing and into the microwave chamber to properly cool the magnetrons and the plasma lamp bulb during irradiation of the substrate by the lamp system.
In some UV heating and curing applications, the lamp system includes a mesh screen mounted at the open lamp face. The screen is transmissive to ultraviolet radiation but is opaque to microwaves. The configuration of the mesh screen also permits the significant airflow of cooling air to pass therethrough and toward the substrate.
In other applications, the substrates irradiated by the UV lamp may require a clean environment, such as in a curing chamber, so that the substrate will not be contaminated during the heating and curing process by contaminants that may be carried by the cooling air. The substrate may also be somewhat delicate and may therefore be susceptible to damage by significant flow of cooling air that would impinge upon and possibly disturb the substrate. In other applications, the substrate may also be adversely affected by excessive heat which may be generated by the plasma lamp bulb during the irradiation process. In such applications, a quartz lens has been used to protect the substrate from the flow of cooling air, while facilitating irradiation of the substrate by the lamp. Such a system is described in U.S. Pat. No. 6,831,419 to Schmitkons et al., the disclosure of which is incorporated by reference herein in its entirety.
In conventional microwave-excited UV lamp systems, cooling air is provided from a source, such as a blower, fan or other appropriate air moving device, and is supplied at a predetermined flow rate, such as about 350 CFM. The lamp system will generally include a simple, on/off-type pressure switch positioned in the air stream to ensure that an adequate flow of air is provided to cool the magnetrons and the ultraviolet lamp. In such systems, the pressure switch shuts down the UV lamp system to avoid overheating when an insufficient amount of airflow is detected. Because pressure switches are generally not very accurate, the actuation pressure of the switch is set to correspond to a flow rate that is well below the optimum operating pressure of the lamp head to ensure that system will not fault at a pressure higher than the lamp rating.
In certain applications, it is desired to adjust the power of a UV lamp system to obtain particular results, or to place the system in a “stand-by” mode. Over cooling of the UV lamp may result when the power is reduced due to the constant flow of cooling air across the lamp, which has generally been set to correspond to a particular power level of the lamp. Additive-type UV bulbs generally require temperatures that are close to the maximum allowable temperature of the bulb to ensure that the additive materials remain in the plasma and thereby produce the desired spectrum. When these additive-type systems are operated at reduced power, the bulbs can become overcooled such that the additives are not maintained in the plasma, thereby resulting in decreased efficiencies and/or undesirable results.
A need therefore exists for a UV lamp system that addresses these and other deficiencies of the prior art.